This invention relates generally to the supply of electrical power to electronic equipment and more particularly to the protection of such equipment from the effects of power disturbances of a transient or temporary nature.
Electrical power interruptions often occur as a result of power plant operations or as a consequence of equipment malfunction or damage. In order to avoid damage to equipment and/or ensure safe operation of certain equipment, it is necessary to provide a waiting period after restoration of power of a duration in excess of some critical interval of time to prevent immediate supply of relatively high operating voltage to the equipment. For example, in certain radar control circuits a low voltage must be initially supplied to the transmitter tube filaments during a warm-up waiting period before high operating voltage is applied. Otherwise, the application of a high voltage to an electron tube for radar operation while the tube heater filaments are cold, may cause catastrophic failure. Thus, time delay relays have been utilized to ensure equipment stabilization by preheating or cooling sensitive components of the equipment during the same fixed waiting period, such as five minutes, before the high voltage is applied. The fixed waiting period often accounts for equipment shutdown with extended loss of its capability, despite very short or momentary power interruptions, because the duration of such waiting period is preset to assure safe operation under worst scenario conditions.
It is therefore an important object of the present invention to vary the time delay waiting interval before a high operating voltage is applied to electronic equipment so to accommodate different power disturbances without excessive equipment shutdown.